Usually observed at birth or shortly thereafter in 94% of patients, in other reports, patients did not develop skin lesions until 3 months or even 2 years after birth. Females are typically affected more often than males (64%).

Studies have recorded an incidence of about 3–5 cases per 1,000 newborn babies.

Ultraviolet light from the sun causes premature aging of the skin and skin damage that can lead to melanoma. Some scientists hypothesize that overexposure to UV, including excessive sunlight, may play a role in the formation of acquired moles. However, more research is needed to determine the complex interaction between genetic makeup and overall exposure to ultraviolet light. Some strong indications that this is so (but falling short of proof), are:

- The relative lack of moles on the buttocks of people with dysplastic nevi.

- Freckles (spots of melanin on the skin, and distinct from moles) are known to be influenced by sunlight.

Studies have found that sunburns and too much time in the sun can increase the risk factors for melanoma. This is "in addition to" those who have dysplastic nevi being at higher risk of this cancer (the uncertainty is in regard to acquiring "benign" moles). To prevent and reduce the risk of melanoma caused by UV radiation, the American Academy of Dermatology and the National Cancer Institute recommends staying out of the sun between 10 a.m. and 4 p.m. standard time (or whenever one's shadow is shorter than one's height). The National Cancer Institute also recommends wearing long sleeves and trousers, hats with a wide brim, sunscreens, and sunglasses that have UV-deflecting lenses.

Halo nevi are estimated to be present in approximately 1% of the general population, and are found to be more prevalent in people with vitiligo, malignant melanoma, or Turner syndrome. All races and sexes are equally susceptible to this disease, although a familial tendency has been reported. The average age of onset is in a person's teenage years.

Café au lait spots can arise from diverse and unrelated causes:

- Having six or more café au lait spots greater than 5 mm in diameter before puberty, or greater than 15 mm in diameter after puberty, is a diagnostic feature of neurofibromatosis type I, but other features are required to diagnose NF-1.

- Familial multiple café au lait spots have been observed without NF-1 diagnosis.

- They can be caused by vitiligo in the rare McCune–Albright syndrome.

- Legius syndrome

- Tuberous sclerosis

- Fanconi anemia

- Idiopathic

- Ataxia-telangiectasia

- Basal cell nevus syndrome

- Benign congenital skin lesion

- Bloom syndrome

- Chédiak–Higashi syndrome

- Congenital naevus

- Gaucher disease

- Hunter syndrome

- Jaffe–Campanacci syndrome

- Maffucci syndrome

- Multiple mucosal neuroma syndrome

- Noonan syndrome

- Pulmonary Stenosis

- Silver–Russell syndrome

- Watson syndrome

- Wiskott–Aldrich syndrome

Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.

The prognosis is favorable in most patients with an isolated cutaneous abnormality. In the majority of cases, both the vivid red marking and the difference in circumference of the extremities regress spontaneously during the first year of life. It is theorized that this may be due to the normal maturation process, with thickening of the epidermis and dermis. Improvements for some patients can continue for up to 10 years, while in other cases, the marbled skin may persist for the patient's lifetime.

One study reported an improvement in lesions in 46% of patients within 3 years. If CMTC persists into adulthood, it can result in complaints due to paresthesia, increased sensitivity to cold and pain, and the formation of ulcers.

Few reports included long-term follow up of CMTC into adolescence and adulthood. While about 50% of patients seem to show definite improvement in the reticular vascular pattern, the exact incidence and cause of persistent cases are unknown.

The decision to observe or treat a nevus may depend on a number of factors, including cosmetic concerns, irritative symptoms (e.g., pruritus), ulceration, infection, and concern for potential malignancy.

Experts, such as the American Academy of Dermatology, say that vast majority of moles are benign. Nonetheless, the U.S. National Cancer Institute estimated that 62,480 new cases of melanoma and 8,420 related deaths would appear in the United States in the year 2008.

Data on the chances of transformation from melanocytic nevi to melanoma is controversial, but it appears that about 10% of malignant melanomas have a precursor lesion, of which about 10% are melanocytic nevi. Therefore, it appears that malignant melanoma quite seldomly (1% of cases) has a melanocytic nevi as a precursor.

Café au lait spots are usually present at birth, permanent, and may grow in size or increase in number over time.

Cafe au lait spots are themselves benign and do not cause any illness or problems. However, they may be associated with syndromes such as Neurofibromatosis Type 1 and McCune-Albright syndrome.

The size and shape of the spots do not have any meaning or implications with regards to diagnosis of associated syndromes.

These nevi represent excess growth of blood vessels, including capillaries.

- Nevus simplex (also known as a stork bite, salmon patch, or Nevus flammeus neonatorum)

Spitz nevi are uncommon. Their annual incidence was estimated in a coastal population of sub-tropical Queensland to be 1.4 cases per 100,000 people. For comparison, the annual incidence of melanoma in the same population, which is high by world standards is 25.4 cases per 100,000 people.

Although they are most commonly found on people in their first two decades of life, the age range for people with Spitz nevi is from 6 months to 71 years, with a mean age of 22 years and a median age of 19 years.

Phakomatosis pigmentovascularis is a rare neurocutanous condition where there is coexistence of a capillary malformation (port-wine stain) with various melanocytic lesions, including dermal melanocytosis (Mongolian spots), nevus spilus, and nevus of Ota.

Most stork bites on the face go away completely in about 18 months. Stork bites on the back of the neck usually do not go away.

As halo nevi are only of cosmetic significance, no treatment is required, and patients will be asymptomatic. Although halo nevi are harmless, it is important to monitor the lesion on regular basis. Watch out for any changes in appearance of existing or new halo nevi. If there is any change in appearance or is associated with pain, itch, and infection, a doctor should be consulted immediately to exclude the possibility of melanoma.

Phakomatosis pigmentokeratotica is a rare neurocutanous condition characterized by the combination of an organoid sebaceous nevus and speckled lentiginous nevus. It is an unusual variant of epidermal naevus syndrome. It was first described by Happle "et al". It is often associated with neurological or skeletal anomalies such as hemiatrophy, dysaesthesia and hyperhidrosis in a segmental pattern, mild mental retardation, seizures, deafness, ptosis and strabismus.

Nevoid melanoma is a cutaneous condition that may resemble a Spitz nevus or an acquired or congenital melanocytic nevus.

Port-wine stains were shown to be caused by a somatic activating c.548G→A mutation in the GNAQ gene. An association with RASA1 has also been described.

The congenital melanocytic nevus is a type of melanocytic nevus (or mole) found in infants at birth. This type of birthmark occurs in an estimated 1% of infants worldwide; it is located in the area of the head and neck 15% of the time.

Nevus of Ito (also known as "Nevus fuscoceruleus acromiodeltoideus") is a skin condition with similar features to the Nevus of Ota, but occurring in a different distribution.

Mucinous nevus (also known as "Nevus mucinosus") is a rare cutaneous condition characterized by hamartoma that can be congenital or acquired.

Nevus sebaceus or sebaceous nevus (the first term is its Latin name, the second term is its name in English; also known as an "organoid nevus" and "nevus sebaceus of Jadassohn") is a congenital, hairless plaque that typically occurs on the face or scalp. Such nevi are present at birth, or early childhood, affecting males and females of all races equally. The condition is named for an overgrowth of sebaceous glands in the area of the nevus.

Skin growths such as benign tumors and basal cell carcinoma can arise in sebaceous nevi, usually in adulthood. Rarely, sebaceous nevi can give rise to sebaceous carcinoma. However, the rate of such malignancies is now known to be less than had been estimated. For this reason, excision is no longer automatically recommended.

A capillary hemangioma (also known as an Infantile hemangioma, Strawberry hemangioma, and Strawberry nevus) is the most common variant of hemangioma which appears as a raised, red, lumpy area of flesh anywhere on the body, though 83% occur on the head or neck area. These marks occur in about 10% of all births, and usually appear between one and four weeks after birth. It may grow rapidly, before stopping and slowly fading. Some are gone by the age of 2, about 60% by 5 years, and 90–95% by 9 years. Capillary hemangioma is a vascular anomaly.

Capillary hemangiomas occur 5 times more often in female infants than in males, and mostly in Caucasian populations. Additionally, low birthweight infants have a 26% chance of developing a hemangioma.

It is the most common tumor of orbit and periorbital areas in childhood. It may occur in the skin, subcutaneous tissues and mucous membranes of oral cavities and lips as well as in the liver, spleen and kidneys. While this birthmark may be alarming in appearance, physicians generally counsel that it be left to disappear on its own, unless it is in the way of vision or blocking the nostrils.

Pigmented hairy epidermal nevus syndrome is a cutaneous condition characterized by a Becker nevus, ipsilateral hypoplasia of the breast, and skeletal defects such as scoliosis.

A Spitz nevus (also known as an epithelioid and spindle-cell nevus, benign juvenile melanoma, and "Spitz's juvenile melanoma") is a benign melanocytic nevus, a type of skin lesion, affecting the epidermis and dermis.

The name "juvenile melanoma" is generally no longer used as it is misleading: it is not a melanoma, it is a benign lesion; and it can also occur in adults, not only in children.